Telegraph signaling system



sept. 19, '1944.' E, H WEBER, J'R 2,358,610

TELEGRAPH SIGNALING SYSTEM Filed March 12, 1945 ATTORNEY Patented Sept.19, 1944 UNITED STATESl PATENT *OFFICE Y 2,358,610 e y TELEGRAPH'SIGNALlNG SYSTEM i Edward Henry Weber, Jr., Torus River, N. J.,assignor to American Telephone and Telegraph` Company, a corporation ofNew York Application March 12, 1943, Serial No. 478,882

(Cl. Z50- 8) u Claims. YThis invention `relates to Vsignaling systems.

More particularly this invention relates to telegraph systems andespecially to carrier or radio telegraph systems.

In the carrier or `radio telegraph system of this invention, a localoscillator is connected to a source'of carrier telegraph signals so thatthe frequency of the current of the local oscillator is varied so as toequal the frequency of the received carrier current. The localoscillator and the source of carrier telegraph'signals are coupled toeach other by a balanced or Wheatstone bridge system. The source ofthecarrier signals is connected to a diagonal of the bridge While thelocal oscillator is connected to an arm of the bridge. The signalfoutput`circuit is VKconnected to the opposite diagonal of the bridge.

In this system the yreceived carrier Vcurrent-is transmitted through thebridge to the local oscillator and causes the local oscillator to changethe frequency of its generatedcurrent to equal the frequency of thereceived carrier current. The two alternating currents are thus broughtinto synchronism with each other. Theisignal output circuit thenreceivesthe current of the local oscillatorv modulated by the samesignals.'

The modulated current. may thereafter be demodulated in any well knownmanner 'toreproduce the original signals. By confining. the receivedmodulated carriercurrent and the signals of output circuit to oppositediagonals of the bridge, the two are madeconjugate to eachother andtheyare mutually independent of each other except forrthe effectreferred to. Y

V'I'his invention will be better understood from the more detaileddescription hereinafter followingywhen read in connection.. with theaccom- Y panying drawing in which` Figure 1 represents one formof radiotelegraphV transmitting. system to which .the invention may be ,appliedand Fig. 2 represents a `form of radio telegraph receiving system towhich .the invention may also be applied. Y

Referring to Fig. 1 ofthe drawing, a Wheatstone bridge system.WB1 isshown interconnecting an oscillator O1 .with one ormore oscillators O2,O3, etc. The tuned circuit LCl comprises one of the arms of the bridge,the tuned circuit LC2 comprises another of the arms ofthe bridge,Y

and the tuned circuit LCa is divided into tWo parts which may form theremaining two arms'l of the bridge. The coil of the tunedcircuit LCs maybe the secondaryfwindingA of the transformer T1, the primary winding ofWhichiis part of a tuned circuit LC4. The latter tuned circuit `may.

.be connected to either of the oscillators O2 or O3,

as will be described hereinafter.

The tuned circuits LCa and LC4 are coupledv to each other so as toimpress the alternating voltage of either of the oscillators O2 or.Os,'-when kever desired, -upon the diagonal A-B of lthe bridge. Theoscillator O1 is coupled bythe tuned circuit LCS -to the tuned circuitLGr-of'the bridge so as to provide an effective connection of theoscillatorrO1 t'o one. of the armsof` thev bridge as shown. The outputcircuit-'O01 is connected tothe other diagonal C-'D ofthe bridge, thisoutput circuit-supplying currentto a radio transmitter RT of anywell-knoWn-type.' The radio transmitterjRT is connectedfto-an antennacir- .i cuit AN1 ofwell knownV type for transmission of signals toaidistantpo'int'. Y y

A local loop including a batter-y B2; a key K2 and-a relay iWz may beemployed'to control the application of 'current 'from-the' oscillator O2'to the tuned circuitLC4 and "the rest ofthe `bridge WBi, to vary thefrequency of the oscillator O1', as will later befexplained.Asimilariloop including a battery Baa-key Ks and a-rel'ay W3, may-beemployed to control' the :.a'pplication of `'currentfrom anotheroscillator O3 througnthe Ybridgew arrangement to the'same.oscillator-.101 for the same. purpose. The relaysW2-andWsv arefnormally released as shown -so that neither ofthe oscillators O2 or O3will apply' current to the bridge arrangement WBi. If f one of the keysvsuch askey K2 .is depressed, however, therelay W2 will vbecome operated.sopas'totremove the` shunt around oscillator yO2* provided. by. thearmature and back contact-of relay W2. 11n that event the oscillator O2may. supply current to the bridge WB1 over a circuit k'which includesthe'ar mature and back contact of relay. W3 and the A Under normalconditions, whenv the *keys-.2K2 and K3 are released, the oscillatorOrwill supply. current through tuned :.circuit'LCs to the" arm- LC1 ofthe bridge and'thiscurrent lwill .flow inthe .outputfcircuit OCi to.the'radio transmitter RT. Theradio transmitterfRT maybe employedv tomodulate this'currentvupon the. current of a radio frequencyWavein'awell knownmanner for the transmission ofthe modulated .currentlthrough the antenna circuity AN1 `vto adistantfr point. l The oscillatorOrmay, for example; lbea will traverse the output circuit OC1.

not too stable generator of sinusoidal current of any well known type.The circuit of oscillator O1 also may include some kind of keying devicefor controlling the current of oscillator O1 in accordance with signals(the keying device not being shown though of well known type).

When key K2, for examrple, is depressed, the oscillator Ozwill applyvoltage to the diagonal A-B of the bridge WB1 to cause the current ofoscillator O2 to flow serially at any instant through the circuits LC1,L02 and L03 and therefore through all four arms of the bridge. Thevoltage thus generated will send current through the output circuit OC1in one direction and at the same time the voltage generated across thetuned circuit LCz by the same current of oscillator O2 will `causecurrent to flow through the output circuit OC1 in the oppositedirection. As the opposing currents in the output circuit OC1 are ofequal magnitude the resultant current through the output circuit'OCi dueto the current supplied by the oscillator O2'will be practically avnullity. n q

While oscillator O2 is supplying current to the bridge WE1 in responseto the closure of key K2, thevoltage generated by this current acrossthe tuned circuit LC1 of the bridge will also be appliedto theoscillator Or. Y Thisvoltage will act to lock the oscillator O1. in stepwith the oscillator O2 so that the Waves of the two oscillators will bein hsynchronism with `each other. The current of the oscillator O1 willtherefore be changed in frequency to be substantially equal to thefrequency of the current supplied by oscillator O2, but the waves of thetwo oscillators may differ in phase. The current .of `the oscillator O1,being supplied to thefarm LCL-ofthe bridge, will then be transmittedtothe output circuit O C1 of the bridge but the frequencyof this current,

in the output circuit OC1 will Vbe equal to that of the currentof'oscillator vO2. The bridge circuit shown and described herein isalsoV shown and vdescribedin applicants copending applicatransmitter RT,this current similarly emanating from the oscillator O1 but being of thefrequency of oscillator Os. Hence the oscillator Or is caused tooscillate either at its own frequency unaffected by any externalconditions or it may be caused to operate at either the frequencies ofthevoscillators O2 or Oa. Thus the radio transmitter RT will transmitsignals of differentv frequencies in accordance with telegraph signals.y

The resistors R1, R2 and R3 may be added to the circuit if desired inorder that the bridge lmay have equal impedances for currents of allfrequenciesV which may be transmitted therethrough. If the arms of thebridge are all tuned to the same frequency and if selected to exhibitlike characteristics, the bridge will remain balanced under allconditions of its operation.

Although oscillators O2 and O3 and their respective control apparatusW2-K2 and Wa-Ks; are shown in Fig. 1 in proximity to the bridge.-arrangement WBl, they may be located at points'. considerably distantfrom the bridge arrange ment WB1. The lines between oscillators O2 andLO3 may be so long as to have induced therein considerable noise and'other interference. The: arrangement of Fig. l may be employed toeffec-- tively eliminate such noise and other interference; so that theradio transmitter RT may transmit;

the current of oscillator O1 unaffected by the:

noise or interference.

Oscillators O1 and O2 have been described asfl generators of current ofdifferent frequencies, These oscillators may have the same frequencies:

. if so desired. Moreover, all three oscillators may,-

be designed to generate currents having frequen cies of the -same value,although this is by noy means essential to the system. Whenever oscillator O1 is employed to produce current of a fre- 'L quency which isdifferent from the frequenciesr tion,-p entitled Signaling apparatus,SerialNo. 1

478,881,1'lled of even date. Y Y

It will be observed that the oscillator O2 and the outputv circuit OC1are connected in con- Y jugate relationship with each other so thatsubstantially none of the current of oscillator O2 The oscillator O1,however, will alone supply current to theoutput circuit OCi. .Y Althoughthe frequency ofzthe .oscillator O1 continuously follows the frequencyofoscillator O2, vthe current'supplied by oscillator O1 tothejoutput'circuit OC1 will have a substantially constant amplitude forall prac'-V l After key K2 is released, key K1 maybe there-V afterdepressed. In thatcase the oscillator O3 will then supply current to thebridge WBi in a similar manner. This will 'cause oscillator O1 to adopta frequency which is equal to that of oscillator O3. The currentofoscillator Oi-now of afrequencywhich is equal to that of oscillatorOar-will supply current of this frequency to the output circuit OC1 and'to the radio transmitter RT for transmissionv to aldistant point. Y

Thus it will. be observed that the key K2 may be operated totransmit'signal pulses of current tothe output circuit 0C1 and to theradio transmitter RT, the current emanating from oscillator Oi'but beingof the frequency of oscillator O2. Whenkey K3 tis operated Vinaccordance with signals, pulses of current will'be transmitted.LA I

through the output-circuit OC1 to the radio of oscillators O2 and O3,the oscillator O1 may'l return to its normal frequency upon release ofkeys K2 'and K3. f Y

Fig. 2illustrates a radio telegraph receiving system which may includean antenna circuit AN2, a first demodulator-amplifier DM1 to which agenerator or oscillator G may be connected for demodulating receivedradio Waves into intermediate frequencies in a well known manner; aWheatstone bridge arrangement WBi` which is similar to the Wheatstonebridge WB; of Fig. 1 for receiving the currents ofthe intermediatefrequencies; an oscillator O4 which'is tovsupply current of a frequencyequal to that of the received carrier current; an amplifier A1 which isconnected to the'output circuit OC2 ofthe bridge WBz; a demodulator DM2which may be offa heterodyne or an autodyne type; and an output circuitOC3 for receiving the demodulated currents in, for example, the audiofrequency range. The oscillator O4' may be adjusted to produce currentof a frequency of, for example, 501 k. c., which is applied throughtuned circuit LCs to one of the arms L01 of the bridge, as alreadyexplained. This will cause current emanating from oscillator O4 to flowVthrough the output circuit OC2. The current of oscillator O4 will beamplified by amplifier A1 and then demodulated bythe demodulator DM2 soas to produceV a zero frequencyA beating component. Under theseconditions the output circuit OC3 will receive noaudible tone. y

When the antenna AANz receives a radio free quency wave interrupted inaccordance with telegraph signals, the intermediate `frequency com-- thedemodulator DMi'-w`hich may be cf a frequency of 500 k. c.-will beapplied to the'diagonal AV-B of the bridge WBz. This current will reachthe Voscillator O4 as already explained and" cause the oscillator O4 tochangeits frequency so as toy be synchronous with the frequency of thecarrier Wave supplied by' the Ademodulator DM1. Thus the oscillator O4may now becausedto produce oscillations of 'a frequency of, for example,500k. c. The current lof this frequency will be transmitted through theoutput circuit OC2 and through the amplifier A1 to demodulator DM2.'

Demodulator DMz may, for examplaproduceits own current of 501 k. c. fordemodulating the bridge circuit and hence none of the current of thedemodulator DM1 will reach the output circuit OCz. Because of thisconjugacy and also because of the one-way path provided by -theamplifier A1, none of the current of the demodulator DM2 willbe returnedto the demodulator DM1. It will be understood that the oscillator O4 maybe operated either at its own frequency or at any one of severaldifferent frequencies which may be applied to it from the demodulatorDMi.

The radio transmitter of Fig. 1 and the radio receiver of Fig. 2 may beoperated in independent signaling systems which are unrelated to eachother. That-is, the radio transmitter of Figi 1 may be operated inconjunction with any Well known radio telegraph receiver and the radioreceiver of Fig. 2 may be operated in conjunction With any well knownform of radio telegraph` transmitter. l However, the circuits of Figs. 1and:

2, if desired, may form a complete radio telegraph system, as will beunderstood by those skilled in the art. Where several different radiofrequencies may be received at different times by the receiving antennaANZ the frequency of oscillator O4 will be changed to match andcorrespond with the carrier wave received by the antenna ANz at anyinstant. The resulting beat note will be of a frequency whichcorresponds to the particular radio wave received by the system. Theoutput circuit OC3 may include well known selecting devices (not shown)to distinguish a beat note of one frequency from that of anotherfrequency.

In Figs. 1 and 2 the oscillators O1 and O4 are shown connected to tunedcircuits LCs and LC1 of the balanced bridge system. It will beunderstood that either tuned circuit LCs or bothl of these tunedcircuits may be incorporated as part of the oscillators O1 and O4, asWill be apparent to those skilled in the art. As the oscillators O1 andO4 may be of any one of many different types, their circuits are notshown in detail because the oscillators themselves do not comprise thisinvention.

Although Fig. 2 has been described :as a radio telegraph receivingsystem, the same general arrangement may be employed for receiving anddetecting frequency modulated signals. If lig 2 'is used in a frequencymodulated system, the

25ste-.Seftues; off 'the intermediateifrequency. p y Thus Vtheoscillator O4 will produce current of a frequency which changes inaccordance vwith the received frequency modulated current.

However, the current of oscillator O4, though responding tothe frequencyvariationsof the received carrierwave, will supply'current ofsubstantially'constant amplitude. Consequently the y limiter-usuallyaccompanying receiving systems drive the oscillator O4 to producecurrent of aY forfrequency modulated signals may be omitted. Thedemodulator DMZ will necessarily comprise any Well known 4type ofdetector for converting the frequency variations of the current ofVoscillator O4 into audible signals. v

Thus the circuit of Fig. 2 may be" employed to variable frequency tocorrespond to the frequency variations of received frequency modulated.signals. These frequency variations willA f be detected by thedemodulating apparatus DMz without alimiter. Y The bridge circuit WBzwilly operate 3withoscillator Oa? to substantially reduce noise or otherinterfering effects.

While this invention has been shown and describedl in certainparticularmerely for the purpose of illustration, it will be understood that thegeneral principles of this invention may be applied to other and widelyvaried organirations without departing from the spirit of the inventionas defined in claims.

What is claimed is:

1. In a-signalingsystem', the combination of a first oscillator, meansAfor interrupting the current of theviirst oscillator in accordancewithsignals, Ya second oscillator of a frequency different from that ofthe iirst oscillator, means comprising a balanced bridge circuitcoupling said K first oscillator with said second oscillator forcoupling said oscillator with said receiving means for applying thereceived modulated carrier current to said oscillator to vary thefrequency of the current generated by saidoscillator to continuallyequal the frequency of the received carrier current,'and means forderiving the signals from the current of said oscillator.

3. In a signaling system, the combination of an oscillator of variablefrequency, a source of carrier current modulated by signals, a bridgecircuit coupling said source and said oscillator so that the frequencyof the current obtained from said oscillator will always equal thefrequency of said carrier current, and means for obtaining the currentof said oscillator and detecting the signals therefrom.

4. In a telegraph signaling system, the combination of first and second,oscillators, the current of said first oscillator being interrupted inaccordance with signals, a Wheatstone bridge,

Wheatstone bridge whereby the current of the embodiments k the appended'second Y V.oscillator n is; ysynchronized in wfrequency Withthe currentof the rstlos'cillator andthe current of said second oscillator isinterrupte'd` by the same signals, and means Aconnected to the otherdiagonal of the bridge'f'or derivingthe signals from lthe current ofthesercond oscillator.

, 5. In a radiotelegraph signaling system uponv which is impressedcarrier current interrupted in accordance with signals, means forVderiving 4the signals from said interrupted carrier current,

saidfrmeans including an oscillator, aVWheatstone bridge to whichsaidoscillatorv-is connected as one arm thereof, means ,fgr impressingthe received interrupted carrier current upon av diagonal of the bridge,and apparatus connected to the other diagonal of the bridge fordernodulating and reproducing the signals.

6. In a telegraph system for reproducing the signals present in the formof interruptions of carrier current, the combination of an oscillator,means responsive to the received interrupted carrier current to changethe1frequency of the current of'said oscillator to equal Vthe frequencythe received carrier current and interrupting.

the current of said oscillator in accordance with said signals, saidmeans comprising a balanced bridge circuit coupling said oscillator to.said sources of carrier current, and means for detect-- mg the receivedSignals from the current of said oscillator.. r

8.1'In ateleg'raph system, the combination of a, plurality of.. sourcesof carrier current of different frequ'encieaineans for interrupting thecurrent of anyone of said sources in accordance with telegraph signals,an oscillator,'means forV changing the frequency of the oscillator toequal the frequency of any one of the received interrupted carriercurrents, said latter means comprising a balanced bridge circuitcoupling said oscillator to said sources of carrier current, andmeansfor observing the oscillator current in-H terrupted in accordance withthe same signals.

9L In a 'telegraphsystem the combination of I a plurality of sources ofcarrier currentV of Vdif ferent frequencies, means for interrupting`theA currents of said sources in accordance with signals, an oscillator,a Wheatstone bridge `system `upon one diagonal of which is impressed thecurrent of any one of said sources interrupted by said signals, theoscillator being connectedrto an arm of said bridge so as to be lockedVin step with the carrier current received by said bridge-diagonal, and acircuit connected to the other diagonal of the bridge Yfor receiving thecurrent of the oscillator interrupted by said signals.

, 10. In a telegraph system, the combination of a lsource of signals inthe form of a carrier wave interruptedrin accordance with the signals,an`

oscillator, means coupling said oscillator with said sourcerof signalssothat the carrier Wave of said source will vary and determine thefrequency of thev oscillator, said means including means for derivingthe current of the oscillator interrupted by the same'signals, and meansfor demodulating the current of the oscillator interrupted by saidsignals to reproduce said signals. e

EDWARD HENRY WEBER, JR.

